The present invention relates to a feeder unit for a sheet-processing machine, and, more particularly to a feeder unit suitable for sheet-fed rotary printing machines (e.g., flexographic printing machines) having printing cylinders and transfer drums, offset printing machines and sheet-fed coating machines (e.g., varnishing machines).
A feeder unit for a sheet-processing machine is disclosed in DE 43 43 616 A1 in the context of a modular printing machine system. This feeder unit includes, inter alia, a first feed drum that cooperates with the printing cylinder of a printing unit. With reference to a plate cylinder of the printing unit which is single-sized, the feed drum is double-sized (i.e. the feed drum has a diameter and, in turn, a circumference twice that of the plate cylinder) and has two gripper systems arranged about its periphery. Additionally, a second feed drum is arranged upstream and offset vertically in the sheet delivery direction from the first feed drum. The second feed drum is the same size as the single-size plate cylinder. A third single sized feed drumxe2x80x94again with reference to the single-size plate cylinderxe2x80x94is likewise arranged vertically offset and upstream of the second feed drum. The third drum is operatively connected to a feed table that is inclined at an angle. This feed drum arrangement operates as a sheet accelerating system for a feeder unit in a preferred high-version unit construction, such as for processing board. The printing machine system is disclosed as being suitable for processing both board and paper. However, a normal feeder unit for paper processing presumably has to be exchanged with a high-version feeder unit as a complete subassembly in order to process board material.
One disadvantage with this type of feeder unit is that it is relatively complicated due to the large number of drums that are utilized. Moreover, the large number of sheet transfers between drums and the curved sheet paths defined by the drums have a detrimental effect on the sheet run. Another disadvantage of this construction is that the normal feeder unit must be replaced before the feeder unit can be used as a high-stack feeder.
Rotating pregrippers are also known in the art. For example, a sheet feeder for printing machines is disclosed in DE-B 2 063 618 which includes, inter alia, a rotating pregripper drum with a feed table that is arranged upstream and inclined in the delivery direction. This pregripper drum has two diametrically arranged gripper systems each of which can dip or pivot into the body of the drum. In a first disclosed embodiment, the feed of sheets is carried out with the pregripper drum and a transfer drum interposed upstream of a downstream printing cylinder. In a second disclosed embodiment, the pregripper drum is arranged directly upstream of a printing cylinder. The front guides of the pregrippers are integrated into the feed table and are pivotable from below.
Likewise, a rotating pregripper for printing machines with two sheet holding systems (gripper systems) is disclosed in DE 27 18 314 A1. This reference discloses a feed table arranged upstream of the rotating pregripper in the delivery direction and a feed drum of equal diameter arranged downstream. In this configuration, the pregripper rotates at half the speed of the feed drum. The gripper systems are configured on the pregripper in such a manner that the gripper systems execute an oscillating movement either about the pregripper axis or about a shaft that is mounted eccentrically in relation to the pregripper axis. A portion of the circumferential surface of the pregripper drum projects outwards beyond the level of the feed table in such a manner that detrimentally effects the sheet feed.
In view of the foregoing, an object of the present invention is to provide a feeder unit for a sheet-processing machine which overcomes the problems with conventional feeder units, and more particularly permits a simple modular construction and allows improved sheet feeding of the printing materials.
In accordance with these and other objects of the present invention, a feeder unit is provided which can be constructed as a standard subassembly (module) comprising a feeder, a feed table and a feed drum whichxe2x80x94with reference to a single-size blanket or plate cylinderxe2x80x94is at least double-size (i.e., having a diameter and, in turn, a circumference twice that of the blanket or plate cylinder). The feeder unit is arranged directly upstream of a processing unit, such as a printing or coating unit, so as to, for example, eliminate the need for special feeder printing units and allows the processing machine to be assembled entirely in a series design using essentially identical processing units. Therefore, all the printing units (e.g., offset and/or flexographic printing units, or varnishing units) can be arranged in a modular fashion as identical units within a sheet-processing machine. The modular construction provides the further advantage that the processing machine and the feeder unit itself can be produced more economically and with a minimal parts expenditure. Moreover, the feeder unit can be universally implemented with, for example, offset printing machines, flexographic printing machines or coating machines.
The feed drum also can be constructed such that it always rotates in the delivery direction thereby eliminating the time required for the return swing in conventional oscillating systems. Thus, the present invention allows the operating speed of the machine to be increased. In this case, changes on the flanks on the drive systems also do not occur thereby promoting quiet operation of the machine. Reverse-acting torques on the drive gear train are also noticeably reduced, and the drive itself has a relatively simple construction.
Improvement in the feeding of the sheets provides a further advantage of the present invention. Specifically, the inclined, or preferably horizontal, configuration of the feed table in conjunction with the double-size or larger feed drum that is arranged in relation to the feed table produce, as a result of the relatively large drum diameter, substantially less curving of the sheet-like printing material, as compared to when a single-size feed drum is used. Thus, the feeder unit can be universally used for processing relatively thin printing materials and also thicker printing materials, such as board or sheet metal, regardless of the resilient characteristics of the printing material.
The double-sized or larger feed drum is arranged on or offset vertically above a horizontal line formed by the axes of all the printing cylinders of the processing units. This arrangement allows the feed to have a high-stack configuration, even when a horizontally arranged feed table is used. There is no need to perform a complicated procedure in order to replace a normal-stack feeder with a high-stack feeder.
When a horizontally arranged feed table is used, the sheets separated by the feeder are fed to the feed drum in a horizontal delivery plane in a staggered and overlapped relation. Therefore, damage to the printing material, which, for example, can occur at the transition from the feeder to the feed table, can be avoided.
The feed table is preferably constructed as a suction-belt table. When a horizontal arrangement of the suction-belt table is used, the present invention provides the advantage that the overlapping stream on the suction-belt table can be shortened (shortening of the delivery path). Therefore, the length of the feed table can be reduced and, for example in the case of a stoppage, fewer rejects occur.
These and other features and advantages of the invention will be more readily apparent upon reading the following description of a preferred exemplary embodiment of the invention and upon reference to the accompanying drawings wherein: